Compounds of Groups IB, IIIA and VIA, especially copper indium diselenide (CIS) and copper indium gallium diselenide (CIGS), have been studied as semiconductor materials for a number of thin-film semiconductor applications. One key application is their use as light absorbing materials in solar cell components. The elements forming these compounds are relatively common and fairly inexpensive, and when formulated and processed into light absorbing materials (e.g., CIS and CIGS), they are highly efficient in converting solar energy to electrical energy.
Unfortunately, cost effective methods of fabricating these light absorbing materials, especially in the form of thin films, have been elusive and limited at best. Most current fabrication methods of light absorbing materials (e.g., CIS and CIGS) rely on vacuum deposition techniques (e.g., physical vapor deposition), which are generally expensive and labor-intensive.
Recent advances in the thin film technology involve the use of liquid precursors to deposit precursors of light absorbing materials. Liquid precursors for use in thin film deposition represent less expensive alternatives to vacuum deposition technology. Liquid precursors provide distinct advantages over conventional vacuum deposition technology including higher throughput, lower cost and more efficient material utilization. In addition, liquid precursors are compatible with a broader range of substrate types and surface morphologies including very large substrates or those having considerable flexibility.
Liquid precursors are generally formulated to contain a combination of metal and a multinary chalcogenide material each selected, respectively, from the elements of Group IB, Group IIIA and Group VIA, utilizing hydrazine as a solvent. Upon deposition, the liquid precursor converts into a desired solid precursor or a metal chalcogenide through the application of heat. The deposited solid precursor can then be processed via suitable means in combination with other solid precursors to produce the final light absorbing material (e.g., CIS and CIGS). Of particular interest is the use of precursor solutions for deposition of indium selenide, gallium selenide and indium gallium selenide.
In the past, reducing agents have been used to prepare such liquid precursors. The use of hydrazine as a solvent is problematic. Hydrazine is a volatile, corrosive liquid that is expensive, highly toxic and dangerously unstable. Its use therefore is strictly controlled. For the same reasons, hydrazine-containing liquid precursors require special care and handling, and implementation of extensive safety measures. Thus, the cost and difficulty associated with making and using hydrazine-containing liquid precursors is considerably high.
In view of the foregoing, there is a need in the art for liquid precursors and methods of preparing the same that are safer, simpler and more cost efficient, while retaining the desirable properties of liquid precursors.